A process for treating hydrocarbon-containing effluents that comprise isoalkanes to reduce the hydrocarbon concentration at least partly is described, characterized in that in the presence of a suitable substrate, a Corynebacterium urealyticum CIP-I-2126 bacterium is grown, and the hydrocarbons that are contained in the effluents are degraded by the biomass of said bacteria that is thus produced.
Application for pollution control of water and soil contaminated by hydrocarbons and optionally by ethers that come from a gasoline, kerosene and/or gas oil fraction.
The invention relates to microorganisms that are capable of degrading in particular isoalkanes and ethers. It pertains particularly to the industries for treatment of water and soil contaminated by petroleum fractions, such as gasoline, gas oil or kerosene.
The prior art is illustrated by Patents FR-A-2 007 109, U.S. Pat. No. 5,679,364, U.S. Pat. No. 4,432,887, and U.S. Pat. No. 5,334,533.
For gasolines, the elimination of tetraethyl lead had the effect of developing new formulations in which the isoalkanes and oxidized products, such as ethers, are important components. Actually, the isoalkanes such as isooctane (2,2,4-trimethylpentane) and the oxidized compounds, such as ethers like methyl-tert-butyl ether (MTBE), but also ethyl-tert-butyl ether (ETBE) and tert-methyl amyl ether (TAME), make it possible to impart good octane ratings to the gasolines.
Accidental dumping of these products leads to pollution of the soil and groundwater or surface waters. The aromatic compounds such as benzene, toluene, ethylbenzene, and xylene are easily degraded by the microflora of the soil (Tsao, C.-W. et al. 1998. Appl Environ Microbiol 64: 4924-4929; Zhang, W. and Bouwer, E. J. 1997. Biodegradation 8: 167-175; Alvarez, P. J. J. and Vogel, T. M. 1991. Appl Environ Microbiol 57: 2981-2985). Conversely, the compounds that comprise highly substituted carbon atoms are very resistant to biodegradation by the microorganisms in the environment.
The literature that relates both to the biodegradation of highly substituted isoalkanes and to the biodegradation of alkyl ethers that are used in the gasolines indicates that the metabolism of these compounds in the environment is not a common phenomenon. It is relatively slow under aerobic conditions and under anaerobic conditions, even nonexistent for isoalkanes under anaerobiosis (McKenna, E. J. 1972. In: Degradation of Synthetic Organic Molecules in the Biosphere. National Acad Sci, pp. 73-97; Nakajiama et al. 1985. Agr Biol Chem 49: 1993-2002).
A new bacterium was discovered that makes it possible to degrade isoalkanes, particularly the most resistant that have in particular a quaternary carbon atom, such as 2,2-dimethylpentane, 2,2,4-trimethylpentane and polysubstituted alkanes such as 2,3-dimethylpentane and 2,3,4-trimethylpentane, as well as ethers.
One of the objects of the invention is to describe a process that uses this new bacterium to degrade hydrocarbons and particularly isoalkanes and alkanes as well as other hydrocarbons in gaseous or aqueous effluents so that the releases are compatible with the standards in force.
Another object is to degrade at least in part a gasoline-type hydrocarbon fraction that is contained in effluents that can contain ethers such as MTBE, ETBE and/or TAME.
Another object is to degrade at least in part a hydrocarbon fraction that is contained in the kerosene type effluents and/or gas oil type effluents.
Another object of the invention is the use of this bacterium for the decontamination in situ of polluted soil. This new bacterium has been filed Feb. 8, 1999 at the Institut Pasteur (CNCM of the Institut Pasteur, 25, rue du Docteur Roux, F75724, Paris Cedex 15) in the name of Corynebacterium urealyticum CIP-1-2126.
More specifically, the invention relates to a process for treatment of hydrocarbon-containing effluents that comprise isoalkanes to reduce at least in part the hydrocarbon concentration, characterized in that in the presence of a suitable substrate, a Corynebacterium urealyticum CIP-I-2126 bacterium is grown, and the hydrocarbons that are contained in the effluents are degraded by the biomass of said bacteria that is thus produced.
The bacterium according to the invention was previously selected in a phreatic layer that was formerly contaminated by an advantageously unleaded gasoline fraction before being inoculated in the presence of said effluent that contains hydrocarbons.
According to a characteristic of the process, the growth substrate can comprise said effluents that contain hydrocarbons.
According to a variant, the substrate can be selected from the group that is formed by alcohols, preferably primary or secondary alcohols, with 2 to 8 carbon atoms, optionally hydroxylated aliphatic monacids or polyacids, with 2 to 8 carbon atoms, optionally hydroxylated aliphatic monoacid or polyacid salts with 2 to 8 carbon atoms, isooctane and mixtures thereof.
Excellent results were obtained when the substrate was ethanol, isooctane, the acetate of an alkaline metal salt or ammonium salt, alone or mixed with one another. Isooctane in particular proves to be an excellent substrate.
According to another characteristic of the process, the hydrocarbon concentration in the liquid effluents can be at most equal to 1700 mg/L and preferably between 300 and 1000 mg/L.
It was already mentioned that the effluents can additionally contain hydrocarbons of a gasoline, kerosene or gas oil fraction, at least one ether that improves their properties. The gasoline fraction thus preferably can contain the MTBE, ETBE, TAME or mixture thereof to improve its octane rating.
Under these conditions, it is possible to degrade the effluents that contain the hydrocarbons and at least one ether by the biomass of bacteria produced in the presence of at least one colony that is selected from the group that is formed by Pseudomonas cepacia CIP I-2052, Arthrobacter globiformis ATCC 53596, Bacillus vaccae JOB5 for mineralizing essentially the entire ether.
The concentration of the ether in the effluent can be between 50 and 1500 mg/L and preferably between 100 and 500 mg/L.
The ex-situ techniques of biological clean-up of the pollution relate to soil and groundwater. The treatment of the soil uses the aerating technique (venting) that makes possible the recovery of volatile products in the form of a gas phase. These gaseous effluents, just like the liquid effluents, polluted groundwater, for example, can then be treated by a biofilter. They are introduced into the biofilter, for example, in which the bacteria are attached to a mineral substrate or organic substrate, or else they can be added as an inoculum to sewage purification plant sludges. The effluents can be enriched with isooctane to improve the growth stage.
According to an embodiment, it is possible to use the colony according to the invention in the presence of air in at least one biofilter that is fed with the effluent from which pollution is to be removed. According to a more advantageous mode, it is preferable to use a system of two or more biofilters that are placed in series. The first, inoculated with, for example, an aerobic microflorum of a sewage purification plant sludge, mainly degrades the aromatic compounds, while the second, inoculated with at least the CIP-I-2126 colony, degrades the refractory compounds such as the isoalkanes and the cycloalkanes in the presence of air or oxygen. The feed rate is, for example, between 0.1 and 2 L/L of biofilter/hour. The effluent, from which hydrocarbons and optionally ethers have been removed at least in part, is then drawn off.